Variable pressure relief valve

1. A single stage, electrically controlled variable pressure relief valve assembly, comprising: a housing having a reference axis defined therein, a stepped bore defined therethrough along the reference axis, an inlet port, an outlet port and a bleed port in communication with the stepped bore, the stepped bore has a first diameter of a predetermined size and a second diameter of a larger predetermined size to established a differential area therebetween and the inlet and outlet ports open into the larger second diameter; an electrically controlled coil assembly having an armature disposed therein and being sealingly secured to the housing at one end of the stepped bore with the armature of the electrically controlled coil assembly being disposed generally parallel with the reference axis of the housing; a valving element assembly slideably disposed in the stepped bore of the housing to define a fluid chamber between the valving element assembly and the armature of the electrically controlled coil assembly, the valving element assembly includes a sleeve member and a plug member, the sleeve member has first and second ends, a blind bore having a bottom, first and second ports, and a peripheral surface having first and second spaced apart peripheral lands, the first end of the sleeve member is in contact with the armature of the electrically controlled coil assembly and the blind bore in the sleeve member extends from the second end along the reference axis of the housing to the bottom thereof, the first peripheral land is spaced from the first end of the sleeve member and of a size to be slideably received within the first diameter of the housing and the second peripheral land is of a size to be slideably received in the larger second diameter of the housing to form a force control chamber therebetween, the first port of the sleeve member extends from the peripheral surface thereof to the blind bore and the second port thereof extends from the second peripheral land to the blind bore and both of the first and second ports are oriented generally perpendicular to the reference axis of the housing, the plug member has a bore defined therein and has first and second portions, the first portion has a diameter that extends into the blind bore and is sealingly secured to one end of the blind bore, the second portion of the plug member has a diameter larger than the diameter of the first portion thereof and is sealingly disposed in the blind bore of the sleeve member to define a flow control chamber between a portion of the blind bore of the sleeve member and the diameter of the first portion of the plug member, the flow control chamber extends parallel with the reference axis of the housing and is in continuous communication with the first and second ports of the sleeve member, a bleed control orificed passageway is disposed between the fluid chamber located between the valving element assembly and the armature and the bore within the plug member; a spring bumper plug secured in the stepped bore of the housing to form a spring chamber and located at the end thereof opposite to the electrically controlled coil assembly; and a spring member disposed in the valving element assembly between the sleeve member and the bumper plug and operative to urge the valving element assembly towards the electrically controlled coil assembly, the bleed port in the housing communicates with the spring chamber.

2. The single stage, electrically controlled variable pressure relief valve assembly of claim 1 wherein the difference in size of the first and second peripheral lands on the sleeve member in the force control chamber establishes a differential area thereon that is in continuous communication with the inlet port of the housing.

3. The single stage, electrically controlled variable pressure relief valve assembly of claim 2 wherein the second port of the sleeve member is in selective communication with the outlet port of the housing to meter flow out of the valving element assembly.

4. The single stage, electrically controlled variable pressure relief valve assembly of claim 3 wherein the first port of the sleeve member is in continuous communication with the inlet port of the housing.

5. The single stage, electrically controlled variable pressure relief valve assembly of claim 3 wherein the first port of the sleeve member is in selective communication with the inlet port of the housing.

6. The single stage, electrically controlled variable pressure relief valve assembly of claim 3 wherein the inlet and outlet ports of the housing are oriented generally perpendicular to the reference axis of the housing.

7. The single stage, electrically controlled variable pressure relief valve assembly of claim 2 wherein the differential area on the sleeve member of the valving element assembly is formed by a surface that forms an acute angle with respect to the reference angle of the housing.

8. The single stage, electrically controlled variable pressure relief valve assembly of claim 7 wherein the differential area on the stepped bore of the housing is formed by a surface that forms an acute angle with respect to the reference angle of the housing.

9. The single stage, electrically controlled variable pressure relief valve assembly of claim 8 wherein the acute angle of the differential area surface on the sleeve member is larger than the acute angle of the differential area surface on stepped bore of the housing.

10. The single stage, electrically controlled variable pressure relief valve assembly of claim 2 wherein the second port of the sleeve member is in continuous communication with the outlet port of the housing and the first port of the sleeve member is in selective communication with the inlet port of the housing to meter flow into the valving element assembly.

11. The single stage, electrically controlled variable pressure relief valve assembly of claim 2 wherein the bleed control orificed passageway is formed by a bleed passage defined in the sleeve member adjacent the bottom of the blind bore, a bleed control chamber defined at the bottom of the blind bore, and a bleed orifice defined in the first diameter of the plug member.

12. The single stage, electrically controlled variable pressure relief valve assembly of claim 2 in combination with a fluid system to form a work system, the fluid system having a reservoir connected to the outlet port of the housing, a source of pressurized fluid connected to the inlet port of the housing, a fluid actuator operatively connected to source of pressurized fluid to move a load and a controller operatively connected to the electrically controlled coil assembly.

13. The single stage, electrically controlled variable pressure relief valve assembly of claim 12 wherein the work system is a fan drive system and the fluid actuator is a fluid motor and the load is a cooling fan.

14. The single stage, electrically controlled variable pressure relief valve assembly of claim 12 wherein the work system is an implement system and the fluid system includes a directional control valve operative to control the flow of the fluid from the source of pressurized fluid to the fluid actuator.

15. The single stage, electrically controlled variable pressure relief valve assembly of claim 12 wherein one of a pressure sensor and a speed sensor is operatively disposed within the work system.

16. A single stage, electrically controlled variable pressure relief valve assembly comprising: a housing having a reference axis defined therein, a stepped bore defined therethrough along the reference axis, an inlet port, an outlet port and a bleed port in communication with the stepped bore; an electrically controlled coil assembly having an armature disposed therein and being sealingly secured to the housing at one end of the stepped bore with the armature of the electrically controlled coil assembly being disposed generally parallel with the reference axis of the housing; a valving element assembly slideably disposed in the stepped bore of the housing and the electrically controlled coil assembly, the valving element assembly includes a sleeve member and a plug member, the sleeve member defines a blind bore and has first and second ends, first and second ports oriented generally perpendicular with the reference axis of the housing, and a peripheral surface having first and second spaced apart peripheral lands, the first end of the sleeve member is in contact with the armature of the electrically controlled coil assembly, the first peripheral land is spaced from the first end of the sleeve member and of a size to be slideably received within the stepped bore in the housing and the second peripheral land is larger than the first peripheral land and of a size to be slideably received in the stepped bore in the housing to form a force control chamber therebetween, the first port of the sleeve member extends from the peripheral surface thereof to the blind bore and the second port thereof extends from the second peripheral land to the blind bore, the plug member has first and second portions, the first portion has a diameter that extends into the blind bore and is sealingly secured to one end of the blind bore, the second portion of the plug member has a diameter larger than the diameter of the first portion thereof and is sealingly disposed in the blind bore of the sleeve member to define a flow control chamber between a portion of the blind bore of the sleeve member and the diameter of the first portion of the plug member, the flow control chamber extends parallel with the reference axis of the housing and is in continuous communication with the first and second ports of the sleeve member, the flow control chamber in cooperation with the first and second ports in the sleeve member create a flow path through the valving element assembly; a spring bumper plug secured in the stepped bore of the housing to form a spring chamber and located at the end thereof opposite to the electrically controlled coil assembly; and a spring member disposed in the valving element assembly between the sleeve member and the bumper plug and operative to urge the valving element assembly towards the electrically controlled coil assembly, the bleed port in the housing communicates with the spring chamber.

17. The single stage, electrically controlled variable pressure relief valve assembly of claim 16 wherein the difference in size of the first and second peripheral lands on the sleeve member in the force control chamber establishes a differential area thereon that is in continuous communication with the inlet port of the housing.

18. The single stage, electrically controlled variable pressure relief valve assembly of claim 17 wherein the second port of the sleeve member is in selective communication with the outlet port of the housing to meter flow out of the valving element assembly.

19. The single stage, electrically controlled variable pressure relief valve assembly of claim 18 wherein the first port of the sleeve member is in continuous communication with the inlet port of the housing.

20. The single stage, electrically controlled variable pressure relief valve assembly of claim 18 wherein the first port of the sleeve member is in selective communication with the inlet port of the housing.

21. The single stage, electrically controlled variable pressure relief valve assembly of claim 18 wherein the inlet and outlet ports of the housing are oriented generally perpendicular to the reference axis of the housing.